Detergent tablets



United States Patent US. Cl. 252138 11 Claims ABSTRACT OF THE DISCLOSURE Detergent tablets which contain about 5% to about 30% by weight of a water-soluble synthetic detergent and uniformly distributed granules of sodium tripolyphosphate (STP), which granules are either (1) encapsulated with 2-15 mole percent of STP hexahydrate or (2) intimately intermixed with 0.1-0.5 calcium oxide. The tablets dissolve rapidly in cool (100 F.) water, even after having been allowed to stand in unagitated water.

This application is a division of Ser. No. 438,376 on Detergent Tablets filed by Robert P. Davis and Frank J. Mueller on Mar. 9, 1965, now Patent No. 3,383,321.

This invention relates to detergent compositions in tablet form. More particularly, it relates to detergent tablets which possess good strength and abrasion resistance and are capable of dissolving rapidly even under adverse washing conditions, i.e., in cool water and after standing in unagitated water prior to their use in an agitated system.

Pre-measured amounts of detergent compositions which are compressed into tablet form are well known and have received substantial commercial acceptance. They generally comprise a cleaning agent such as a synthetic detergent or soap and a detergency builder which is generally sodium tripolyphosphate, along with suds builders, soil suspending agents and other ingredients commonly added to cleaning compositions. They are easy to use, avoid the problem of spillage during use, and prevent the use of too much or too little detergent on the part of the consumer. While the use of high pressure tableting easily can make the tablet strong enough to resist breakage, and while the tablets can be made sufficiently abrasion resistant by treating the surface of the tablet with water or certain coating materials, these processing operations tend toincrease the time which is required to dissolve the tablet in water, particularly when cool water must be used. The use of water with temperatures of less than 130 F. is quite common in many parts of the world.

The problem of tablet dissolution rates is particularly acute when the tablet is allowed to stand in unagitated water for a short time prior to beginning the agitation, as when the tablet is placed in a washer while the water and laundry are being added. Under these circumstances the time of dissolution after agitation has begun is often greatly increased. Since this results in a loss of a substantial portion of the cleaning power, this delay in dissolving presents a serious problem to that large number of consumers who normally add the tablets to unagitated water.

Therefore, it is an object of this invention to provide an improved detergent tablet.

3,503,889 Patented Mar. 31, 1970 It is another object of this invention to provide a strong and abrasion resistant detergent tablet which has a rapid speed of dissolution.

It is a still further object of this invention to provide a detergent tablet which dissolves rapidly in cool water and/or after being allowed to stand in unagitated water prior to its use in an agitated system.

Other objects and advantageous features of this invention will be obvious from the following detailed description and claims.

The objects of this invention can be achieved by employing with the granules of sodium tripolyphosphate (hereafter called STP) which are to be used in a tableted detergent composition either of the following:

(1) suificient water to hydrate to the hexahydrate state substantially all of the STP particles which form the surface of the STP granules, which surface hydration is generally accomplished with the addition of suflicient water to hydrate to the hexahydrate state from about 2% to about 15% on a molar basis of the total granular STP present; or

(2) From about 0.1% to about 0.5% of calcium oxide based on the weight of the STP granules.

The effect of such an addition is to decrease the time which is required for the tablet to dissolve in water of any temperature. Thus, higher tableting pressures can be used and stronger tablets can be made which have the same time of dissolution as previous tablets; or an acceptable dissolving rate can be achieved in water of lower temperatures than has been previously possible using a tablet of ordinary strength. Further, and most important, the speed of dissolution of a tablet which has been allowed to stand in unagitated water for a short time prior to the beginning of agitation does not vary substantially from the speed of dissolution of a tablet which is added directly to agitated water. This avoids a serious problem which has plagued the prior art, since it is not unusual for prior art tablets which have been pre-soaked to take from 5 to 10 times as long to dissolve as one which is added directly to agitated water.

While the inventors do not wish to be bound by any particular theory, it is their belief that the reason for slower dissolving times in pre-soaked prior art tablets is as follows. It is the nature of unhydrated STP, when in the presence of a very limited amount of water, to form an unstable supersaturated solution. Beginning shortly thereafter, this supersaturated solution precipitates STP hexahydrate crystals until the normal solubility level of the STP in the water present is reached. When a detergent tablet which contains a relatively high amount of STP is placed in an agitated solution, the surface components of the tablets are rapidly removed by the action of the water. This is both a solubilizing and an eroding action, the latter action removing the particles of the tablet as the binding forces are weakened by the penetration of the water. The particles being thus dispersed, the speed of dissolving is increased. Also, the particle removal process allows the penetration of the water into the tablet to be sufficiently rapid to prevent the above-described supersaturated solutions of STP in water from existing at any point within the tablet for any undue period of time which, in turn, prevents the formation of the precipitated STP hexahydrate crystals as described above. On the other hand, when the tablet is placed in an unagitated system, the eroding action of the water upon the tablet does not take place. However, the water does gradually penetrate into the tablet, thus creating a slowly moving wet-dry interface which surrounds the core of the tablet. The low concentration of water at this relatively stationary interface allows the above-described supersaturation phenomenon to take place and a layer of STP hexahydrate crystals are precipitated out of the supersaturated solution. Under these circumstances, the hexahydrate crystals form bridges between adjacent STP granules, thus creating a shell of interconnected STP granules and STP hexahydrate crystals around a core of the tablet.

In addition to hindering further penetration of water into the tablet, this shell offers substantial resistance to the eroding action of agitated water. Therefore, even if subsequently placed in an agitated system, the movement of the wet-dry interface into the tablet is quite slow and allows a continued formation of a supersaturated STP solution and a continued precipitation of the abovedescribed bridge forming hexahydrate crystals, thus perpetuating the protective shell. It is not uncommon for a tablet with a normal dissolving time of about 60 seconds in an agitated system to have a dissolving time of 500 to 600 seconds when pre-soaked for a short time prior to its addition to the agitated system.

It has been found that a sufiicient delay of the hydration of a substantial amount of the STP in a detergent tablet will alleviate the problems caused by crystallization of the hexahydrate crystals and Will increase the rate of dissolution of the tablet. Most importantly, this delay will prevent formation of the difliculty eroded shell of STP granules and STP hexahydrate crystals around a core of the table in unagitated systems.

The preferred method of accomplishing this result is to treat anhydrous granular STP which is to be used to form detergent tablets with sufficient highly-particulate water to hydrate to the hexahydrate state substantially all of the STP which forms the surface of such granules. When this is done, substantially all of the anhydrous STP granules are encapsulated with STP hexahydrate. When these granules are used to form detergent tablets there is relatively little free, exposed and unhydrated STP available to form a shell of interconnected STP granules and STP hexahydrate crystals. As a result the eroding action of agitated water upon the tablet after pre-soaking is about the same as if the tablet had been placed directly into an agitated system.

The water added to the anhydrous granular STP must be in highly particulate form and in an amount sufiicient to accomplish substantial hydration of the particles forming the surface of each STP granule. Sufficient surface hydration is generally accomplished when at least 2 to 3 mole percent of the granular STP has been hydrated; however, in the preferred practice of this invention from about 6% to about 12% of the STP on a molar basis should be hydrated to the hexahydrate form. The amount hydrated should not exceed 15 mole percent. Employing a moisture content below 15 mole percent makes it easier to formulate an acceptable detergent composition and also makes the finished tablet lighter in weight which is both appealing to the consumer and less expensive for the manufacturer due to decreased shipping costs.

More importantly, however, are the severe processing problems which are experienced at higher moisture levels. With an excess of 15 mole percent granular STP present in the hexahydrate form, the mixture which is to be tableted shows a marked decrease in density. This means that a larger tablet must be made in order to incorporate the desired amount of the detergent materials. Secondly, it is generally the practice in the art today to treat the surface of the pressed detergent tablets with water or other water-containing materials prior to packaging to give the tablet an abrasion resistant coating. This leaves the tablet with a sticky surface until moisture is removed from the coating material. When lower amounts of hydratable salts are present in the tablet, this sticky surface will endure for a considerable period of time, thus requiring an undesirable delay between coating and packaging. Since the unhydrated STP constitutes the bulk of the hydratable salts present in the tablet of this invention, it should not be hydrated to a greater extent than necessary. Lastly, hydration of STP is a highly exothermic reaction; therefore, the temperature of the material being processed is increased progressively with the degree of hydration. For example, when suflicient water is added to hydrate 20% of the granular anhydrous STP, the temperature of the STP can be expected to rise in an amount of about 70 F. to about F. As a result, the material handling considerations are seriously affected and, due to the relatively slow heat loss of solid materials, some sort of cooling would preferably be provided prior to tableting if such a degree of hydration were used. In light of the above reasons the amount of granular STP hydrated should not exceed 15%.

The method of addition of the water to the STP granules for this surface hydration is not critical, so long as the water is added in highly particulate form and intimate mixing of water and STP granules is accomplished. It is preferred to use an atomizer which sprays the water in highly particulate form onto a moving or agitated bed of anhydrous granular STP, or to pass the STP through a humidifying zone of suflicient size, preferably with agitation, to accomplish the required degree of hydration.

Calcium oxide is an effective agent for retardation of the undesirable wet-dry interface around the core of the tablet described above. When from about 0.1% to about 0.5% of powdered and highly particulate calcium oxide, based on the weight of the anhydrous granular STP, is incorporated into a mixture which is to be tableted, sizable increases in dissolving speed are obtained, particularly in the pre-soaked tablet discussed above. The mechanism whereby undesirable hydration of the granular STP in the tablet is retarded, due to the presence of the calcium oxide, is not known. However, it is known that the calcium oxide must be reasonably well interspersed among the STP granules. The calcium oxide particle size is preferably from about 4 to about 40a. The calcium oxide can be mixed with the granular ST P and detergent granules prior to tableting but, in the preferred operation, calcium oxide is mixed with the granular STP prior to its admixture with the detergent granules. In this preferred method a majority of the calcium oxide particles remain admixed with the STP granules, the remainder being imbedded in the softer detergent granules.

It is necessary for successful operation of the present invention that the finished tablet have sufficient interparticle channeling to allow the water to penetrate into the tablet. This penetration serves to loosen the materials near the surface of the tablet, thus enabling the action of the water in an agitated system to more easily disperse and dissolve them. This penetration is also necessary to prevent a troublesome wet-dry interface within the tablet as described above. Therefore, the granules of synthetic detergent and STP which comprise the detergent tablet should be of sufficient size to provide an interparticulate void volume of about 35% to about 60% of the total tablet volume. Such granules should not be so large, however, as to make it diflicult to obtain uniformity in the composition of the tablets, nor difficult to process them. Therefore, the detergent and STP granules for use in this invention should be of such a size that substantially all will pass a standard 6 mesh screen (Tyler) and that at least about will stay on a standard mesh screen (Tyler).

With regard to the STP granules, there is another reason why the above size range must be maintained. As was explained above, it is necessary that each granule, after the water treatment, be substantially coated with hexahydrate crystals. However, to avoid processing, weight and formulation problems also discussed above, the amount of added water should be kept to a minimum. If granules of a smaller size than specified in the preceding paragraph were to be used, the resultant increase in the total surface area of the STP granules would be so large as to prevent the simultaneous achievement of both objectives. To substantially coat each granule of STP with hexahydrate would require the hydration of considerably more than mole percent of the STP present.

Similarly, any optional ingredients for use in this tablet, to be hereafter described, should preferably be of a size comparable to the STP and detergent granules. If substantially different, they should not be used in such an amount as would prevent uniformity of product, or would either interfere with tablet processing or with the formation of the interparticulate channels of the tablet.

The detergent materials which can be used in the detergent granules in the tablets of the present invention are those of the anionic, nonionic, ampholytic or zwitterionic classes. The detergent materials can be per se in the form of detergent granules, as described above, or blended with other tablet components such as builders, as described below, to form detergent granules. At least 5% by weight of the tablet should be such a detergent material in order to provide a tablet of suitable size which has a sufiicient concentration of detergent material for washing purposes. More than 30% by weight of detergent in the tablet will lead to an excessively sticky tablet and this in turn will lead to a deficiency of interparticulate voids, thereby preventing the water from diffusing through the tablet to dissolve said tablet.

Examples of detergent materials which can be used in the tablets of this invention include:

(a) Anionic synthetic detergents: This class of synthetic detergents can be broadly described as the watersoluble salts, particularly the alkali metal salts, of organic sulfuric reaction products having in the molecular structure an alkyl radical containing from about 8 to about 22 carbon atoms and a radical selected from the group consisting of sulfonic acid and sulfuric acid ester radicals. Important examples of the synthetic detergents which form a part of the preferred compositions of the present inven tion are the sodium or potassium alkyl sulfates, especially those obtained by sulfating the higher alcohols produced by reducing the glycerides of tallow or coconut oil; sodium or potassium alkyl benzene sulfonates, in which the alkyl group in a straight or branched chain contains from about 9 to about 15 carbon atoms, and the types described in United States Patent Nos. 2,220,099 and 2,477,383; sodium alkyl glyceryl ether sulfonates, especially those ethers of the higher alcohols derived from tallow and coconut oil; sodium coconut oil fatty acid monoglyceride sulfates and sulfonates; sodium or potassium salts of sulfuric acid esters of the reaction product of one mole of a higher fatty alcohol (e.g., tallow or coconut oil alcohols) and about three moles of ethylene oxide; sodium or potassium salts of alkyl phenol ethylene oxide ether sulfates with an average of about four units of ethylene oxide per molecule and in which the alkyl radicals contain about 9 carbon atoms; the reaction product of fatty acids esterified with isethionic acid and neutralized with sodium hydroxide where, for example, the fatty acids are derived from coconut oil; sodium or potassium salts of fatty acid amide of a methyl taurine in which the fatty acids, for example, are derived from coconut oil; and others known in the art, a number being specifically set forth in United States Patent Nos. 2,486,921, 2,486,922 and 2,396,278.

(b) Nonionic synthetic detergents: This class of synthetic detergents can be broadly defined as compounds produced by the condensation of alkylene oxide groups (hydrophilic in nature) with an organic hydrophobic compound, which can be aliphatic or alkyl aromatic in nature. The length of the hydrophilic or polyoxyalkylene radical which is condensed with any particular hydrophobic group can be readily'adjusted to yield a water-soluble compound having the desired degree of balance between hydrophilic and hydrophobic elements.

For example, a well known class of nonionic synthetic detergents is made available on the market under the trade name of Pluronic. These compounds are formed by condensing ethylene oxide with a hydrophobic base formed by the condensation of propylene oxide with propylene glycol. The hydrophobic portion of the molecule which, of course, exhibits water insolubility has a molecular weight of from about 1500 to 1800. The addition of polyoxyethylene radicals to this hydrophobic portion tends to increase the water solubility of the molecule as a whole and the liquid character of the products is retained up to the point where polyoxyethylene content is about 50% of the total weight of the condensation product.

Other suitable nonionic synthetic detergents. include:

(i) The polyethylene oxide condensates of alkyl phenols, e.g., the condensation products of alkyl phenols having an alkyl group containing from about 6 to 12 carbon atoms in either a straight chain or branched chain configuration, with ethylene oxide, the said ethylene oxide being present in amounts equal to 10 to 25 moles of ethylene oxide per mole of alkyl phenol. The alkyl substituent in such compounds may be derived from polymerized propylene, diisobutylene, octane, or nonane, for example.

(ii) Those derived from the condensation of ethylene oxide with the product resulting from the reaction of propylene oxide and ethylene diamineproducts which can be varied in composition depending upon the balance between the hydrophobic and hydrophilic elements which is desired. For example, compounds containing from about 40% to about polyoxyethylene by weight and having a molecular weight of from about 5000 to about 11,000, resulting from the reaction of ethylene oxide groups with a hydrophobic base constituted of the reaction product of ethylene diamine and excess propylene oxide, said base having a molecular Weight of the order of 2500 to 3000, are satisfactory.

(iii) The condensation products of aliphatic alcohols having from 8 to 18 carbon atoms, in either straight chain or branched chain configuration, with ethylene oxide, e.g., a coconut alcohol ethylene oxide condensate having from 10 to 30 moles of ethylene oxide per mole of coconut alcohol, the coconut alcohol fraction having from 10 to 14 carbon atoms.

(c) Long chain tertiary amine oxides corresponding to the following general formula, R R R N O, wherein R is an alkyl radical of from about 8 to about 18 carbon atoms, and R and R are each methyl or ethyl radicals. The arrow in the formula is a conventional representation of a semi-polar bond. Examples of amine oxides suitable for use in this invention include dimethyldodecyl amine oxide, dimethyloctylamine oxide, dimethyldecylamine oxide, dimethyltetradecylamine oxide, dimethylhexadecylamine oxide.

(d) Long chain tertiary phosphine oxides corresponding to the following general formula RRR"P O wherein R is an alkyl, alkenyl or monohydroxyalkyl radical ranging from 10 to- 18 carbon atoms in chain length and R and R" are each alkyl or monohydroxyalkyl groups containing from 1 to 3 carbon atoms. The arrow in the formula is a conventional representation of a semi-polar bond. Examples of suitable phosphine oxides are:

dodecyldimethylphosphine oxide, tetradecyldimethylphosphine oxide, tetradecylmethylethylphosphine oxide, cetyldimethylphosphine oxide, stearyldimethylphosphine oxide, cetylethylpropylphosphine oxide, dodecyldiethylphosphine oxide, tetradecyldiethylphosphine oxide, dodecyldipropylphosphine oxide,

dodecyldi (hydroxymethyl) phosphine oxide,

7 dodecyldi (2-hydroxyethyl) phosphine oxide, tetradecylmethyl-2-hydroxypropyl phosphine oxide, oleyldimethylphosphine oxide, and 2-hydroxydodecyldimethylphosphine oxide.

(e) Long chain dialkyl sulfoxides containing one short chain (usually methyl) and one long hydrophobic chainwhich can contain from about to about carbon atoms. Examples include:

octadecyl methyl sulfoxide dodecyl methyl sulfoxide tetradecyl methyl sulfoxide.

(f) Ampholytic synthetic detergents can be broadly described as derivatives of alkyl secondary and tertiary amines in which the alkyl radical can be straight chain or branched and wherein one of the alkyl substituents contains from about 8 to about 18 carbon atoms and one contains an anionic water solubilizing group, e.g., carboxy, sulfonate, sulfate, phosphate, or phosphonate. Examples of compounds falling within this definition are sodium 3-dodecylaminopropionate, sodium 3-dodecyl aminopropane sulfonate, dodecyl-beta-alanine, N-alkyltaurines such as the one prepared by reacting dodecylamine with sodium isethionate according to the teaching of United States Patent No. 2,658,072, N-higher alkyl aspartic acids such as those produced according to the teaching of United States Patent No. 2,438,091, and the products sold under the trade name Miranol and described in United States Patent No. 2,528,378.

(g) Zwitterionic synthetic detergents can be broadly described as derivatives of alkyl quaternary ammonium, phosphonium, and sulfonium compounds, in which the alkyl radical may be straight. chain or branched, and wherein one of the alkyl substituents contains from about 8 to 18 carbon atoms and one contains an anionic Water solubilizing group, e.g., carboxy, sulfonate, sulfate, phosphate, or phosphonate. Examples of compounds falling within this definition are 3-(N,N-dimethyl-N-hexadecylammonio) propane-l-sulfonate and 3-(N,N-dimethyl-N- hexadecylammonio -2-hydroxy propanel-sulfonate which are especially preferred for their excellent cool water detergency characteristics.

The alkyl groups contained in said detergent surfactants can be straight or branched and saturated or unsaturated as desired. The above list of detergent surfactants is exemplary and not limiting. Mixtures of the above detergent surfactants can be used.

The STP is used to provide detergency builder properties in the tablet. At least about STP by weight of the tablet should be present to provide good builder action, but more than about 85% by weight of the tablet tends to make the tablet unduly brittle. The ratio of STP to synthetic detergent should be from about 2:1 to about 9:1. A portion of the STP can be added in admixture with the synthetic detergent material and any optional ingredients employed in the form of spray-dried detergent granules. However, an acceptable rate of dissolution will not be achieved if the bulk of the STP is added in this form. Therefore, at least about 20% by weight of the tablet must be STP which is added in admixed, particulate granular form, hydrated as described above, to the composition which is to be tableted; i.e., the tablet should contain from about 20% to about 85% by weight of STP in particulate granular form, hydrated or mixed with calcium oxide as described above, and from 0% to about 65% by weight of STP in addition to the STP in particulate, granular form which has been hydrated or mixed with calcium oxide, such that the total amount of STP is from about 25 to about 85 by weight of the tablet. All of the STP used in the tablet can be in such granular form if desired. Granular STP is preferably from about to about 60% by weight of the detergent tablet, with any balance of STP in the tablet formula preferably being admixed with the detergent material in the form of spray-dried detergent granules.

In addition to the above, various optional ingredients can be used. Such materials as soap, additional builder or sequestrant builder salts are commonly added.

Soap, if used, should be present in an amount not over about 10% by weight of the tablet, and preferably not over about 5%. Soaps acceptable for use in this invention are the ordinary alkali metal soaps such as the sodium and potassium salts of the higher fatty acids of naturally occurring plant or animal esters (e.g., palm oil, coconut oil, babassu oil, soybean oil, castor oil, tallow, whale and fish oils, grease and lard, and mixtures thereof) or of synthetically produced fatty acids (e.g., rosin and those resin acids in tall oil) and/or of naphthenic acids. Sodium and potassium soaps can be made by direct saponification of the fats and oils or by the neutralization of the free fatty acids which are prepared in a separate manufacturing process.

Builder salts, in addition to the STP, are usually desirable in the tablets of this invention. Examples of those most commonly used are the alkali metal carbonates, orthophosphates, pyrophosphates and silicates. Likewise sequestrant builder salts can also be'effectively used in conjunction with the STP. Typical examples of sequestrant builder salts are: (1) alkali metal amino-polycarboxylates such as sodium or potassium ethylene diamine tetra-acetates or nitrilotriacetates; (2) alkali metal salts of phytic acid; and (3) the water-soluble salts of ethane-l-hydroxy- 1,1-diphosphonate, methylene or ethylene diphosphonate, particularly the trisodium and tripotassium salts.

These additional builders or sequestrant builders, or mixtures thereof, can be present up to about 20% by weight of the tablet.

Substantially all of the water present in the tablet, other than that added to hydrate the STP granules, will be associated with the detergent granules. This amount should not exceed about 12% by weight of the detergent granules. Too much moisture will make the detergent granules too soft and, upon tableting, they will distort too readily and fill the interparticulate voids. However, the moisture should not be less than about 3% by weight of the detergent granules. With less than this amount, the detergent granules are too brittle. Upon tableting they will crumble and create an unduly large amunt of small particles which tend to fill the interparticulate voids.

In addition to the above-described ingredients, the detergent tablets of this invention can also contain any of the minor additives commonly used with detergent compositions. These include: bleaching agents, such as watersoluble perborates or persulfates; suds builders, such as fatty acid amides or ethanolamides wherein the fatty acid radical contains from about 8 to about 20 carbon atoms; suds depressers, such as fatty acids or their soaps; soil suspending agents, such as carboxymethyl cellulose; inorganic salts, such as sodium or potassium sulfates or chlorides; and optical brighteners, dyes, and perfumes. The inorganic salts can be present in an amount of up to about 20% by weight of the tablet. The remaining minor ingredients can be present up to a total of about 10% by weight of the tablet.

The tablets of this invention can be prepared by the usual processes of the detergent tableting art. The optional ingredients, if any, can be added independently with the other components prior to tableting or, preferably, incorporated with the synthetic detergent in the form of spray-dried detergent granules. The components are blended in any conventional manner which achieves a reasonably uniform mixture. As a result of the mixing of the ingredients, the anhydrous sodium tripolyphosphate granules, either encapsulated with sodium tripolyphosphate hexahydrate or intimately intermixed with calcium oxide, are substantially uniformly distributed throughout the tablet. The mixture is then pressed into the desired shape by means of a tableting press, preferably one which uses rotating dies and a pressure of from about to about 350 to 450 p.s.i.g. The tablets can then be treated, if desired, with water or other substance designed to increase the strength and abrasion resistance of the tablet surface.

The following examples are given to illustrate the use of the present invention in preparing strong and abrasion resistant detergent tablets which dissolve readily in agitated water, even if allowed to stand for a period of time in unagitated water. However, these examples are not to be interpreted as limitations upon the invention.

EXAMPLE I A series of detergent tablets were prepared which varied only in the degree of percent of hydration of the granular STP which was contained in the tablets. To prepare these tablets, spray-dried detergent granules of the following composition were made, expressed in parts by weight:

Parts (1) Sodium dodecylbenzene sulfonate 10.5 (2) Pluronic L64 (ethylene oxide condensed on a propylene glycol: propylene oxide base. Molecular Samples of these detergent granules and of substantially anhydrous STP granules were screened to determine particle size distribution. It was found that substantially all of the granules passed a standard 6-mesh screen (Tyler) and in excess of 95% stayed on a standard 100-mesh screen (Tyler). The STP granules were then separated into several segments. Each segment, while being agitated, was treated with an atomized water spray to hydrate a portion of the STP to the hexahydrate state. Because of the agitation and the highly particulate nature of the added water, substantially all of the hydration occurred on the surface of the STP granules.

55 parts by weight of the spray-dried detergent granules were then mixed with 45 parts by weight of STP which had been prehydrated to a desired level. Sample tablets were prepared for several different prehydration levels. All tablets were pressed with rotating dies at 200 p.s.i.g. and

.(B) Pro-Soak Speed of Dissolution.This test was very similar to Test (A). However, the wash load and the net bags containing the four tablet samples were placed in the washer prior to the addition of the Water. The washer was then filled and agitation was begun immediately upon completion of the water addition. The same procedures as in (A) were then followed. The dissolving time was measured from the time that agitation was begun. Again, the average of the four samples was taken as the true value for that sample. The filling time of the washer was two minutes.

(C) Tablet Strength-This test was performed on a standard Mullen TesterModel LC, manufactured by B. F. Perkins & Son, Inc. of Holyoke, Mass. The tablet was clamped to a flat tray and a vertical rubber-tipped mandrel placed into contact with the center of the tablet. Pressure was gradually increased until the tablet ruptured. The true value was taken as the average of two such tests conducted at F.

The results are tabulated below, the first column showing the degree of hydration of the STP in the various sets of tablets.

TABLE 1 Percent hydration of Water Pre-soak Strength added STP temp. S.O.D. S.O.D. (lb./in. t0 granules F.) (sec.) (59.0.) rupture) The above results indicate that the tablets of .all samples were of substantially identical strength; that the tablets of samples (2) and (3) dissolve more rapidly than those of sample (1) when placed in agitated water; and that the tablets of samples (2) and (3) dissolve substantially more rapidly than those of sample .(1) when allowed to stand in un'agitated water prior to the beginning of agitation.

EXAMPLE II Sets of sample tablets with the same composition, other than degree of granular STP prehydration, were prepared as described in Example I. These sample tablets were used in the same tests as described in Example I, except that they were also tested at F. to determine the effect of increased water temperature on the respective dissolving times. The results are tabulated below.

allowed to age for in excess of 16 hours at 70-80 P. Then they were used in the following tests.

(A) Speed of Dissolution (S.O.D.).-A standard automatic washer (Kenmore, Model #6204702) was filled with sixteen gallons of water and six pounds of a wash load was added. Each of a set of four sample tablets with the same degree of granular STP prehydration was placed in a separate net bag. These bags were suspended in the washer and the agitation begun immediately. The net bags were withdrawn and observed after 60 seconds and at 60 second intervals thereafter, until no residue was seen in any of the four bags. The time at which the residue in each of the four bags had completely disappeared was recorded, and the average of the four was taken as the Speed of Dissolution for that sample.

The above results indicate that the conclusions drawn from Example I are not dependent upon the temperature of the water.

EXAMPLE III Two sets of detergent tablets were prepared as described in Example I, except that the added granular STP used in the preparation of these samples was substantially anhydrous in order to avoid any influence of prehydrated STP upon the various tablet properties. The sets of samples were identical in content except that 0.2% calcium oxide, based on the weight of the added STP, was added in highly particulate form (about 6, to S t average) to one of the two sets prior to mixing and tableting. These samples were then used in the same tests as described in Example I. The results are tabulated below.

When any of the following synthetic detergent materials are substituted in whole or in part for the sodium dodecyl benzene sulfonate in the above examples, substantially similar improvements in dissolving characteristics are obtained:

(1) Sodium or potassium coconut alkyl sulfates;

(2) Sodium potassium tallow alkyl sulfates;

(3) Sodium or potassium coconut alkyl glyceryl ether sulfonates;

(4) Sodium or potassium coconut fatty acid monoglyceride sulfates and sulfonates;

(5) Secondary sodium or potassium C to C alkyl sulfates;

(6) Sodium or potassium salts of sulfuric acid esters of the reaction product of one mole of C to C alcohols with three moles of ethylene oxide;

(7) Coconut alcohol ethylene oxide condensates having from to 30 moles of ethylene oxide per mole of coconut alcohol;

(8) Condensates of C to C alkylphenols and polyethylene oxide, having from 10 to moles ethylene oxide per mole of alkylphenol;

(9) Dimethyl coconut alkyl amine oxides;

(10) Diethyl coconut alkyl phosphine oxides;

(1 l) 3-hydroxytridecyl methyl sulfoxides;

(12) 3-hydroxy-4-decoxybutyl methyl sulfoxides;

(13) Sodium 3-coconut alkyl amino propionates;

*(14) 3-(N,N-dimethyl-N-tallow alkyl ammonio)-2-hydroxypropane-l-sulfonates; and

'(15) Mixtures of any of the above.

What is claimed is:

1. A detergent composition in tablet form consisting essentially of:

(1) from about 5% to about by weight of a water-soluble synthetic detergent in the form of detergent granules;

(2) from about 25% to about 85% by weight sodium tripolyphosphate, at least 20% by weight of the tablet being sodium tripolyphosphate in the form of granules of anhydrous sodium tripolyphosphate having a surface coating of sodium tripolyphosphate hexahydrate, said sodium tripolyphosphate hexahydrate surface coating being from about 2% to about 15% of each surface-coated granule on a molar basis, said surface-coated granules being uniformly distributed throughout the detergent tablet; and

(3) from about 3% to about 12% moisture by weight of the detergent granules, in addition to the water of hydration of item (2) above;

wherein substantially all of said sodium tripolyphosphate and detergent granules are of sufiicient size to pass a standard 6 mesh screen (Tyler) and at least about 95% of "which will remain on a standard 100 mesh screen (Tyler), and wherein the water-soluble synthetic detergent, sodium tripolyphosphate and moisture are sub stantially uniformly distributed throughout the detergent tablet, said detergent tablet having an interparticulate void volume of about to about 60% of the total tablet volume.

2. The composition of claim 1 wherein the ratio of sodium tripolyphosphate to synthetic detergent is from about 2:1 to about 9:1.

3. The composition of claim 1 wherein the synthetic detergent is sodium alklybenzene sulfonate, having an alkyl chain with from about 9 to about 15 carbon atoms.

4. The composition of claim 1 wherein the synthetic detergent is present in the form of spray-dried detergent granules.

5. A detergent composition of claim 1 wherein each surface-coated sodium tripolyphosphate granules is substantially completely encapsulated by a surface coating of sodium tripolyphosphate hexahydrate.

6. The detergent composition of claim 5 wherein the hexahydrate-encapsulated anhydrous sodium tripolyphospate granules are present in an amount of from about 25 to about by weight of the tablet.

7. The detergent composition of claim 5 wherein the hexahydrate-encapsulated anhydrous sodium tripolyphosphate granules are present in an amount of from about 35% to about 60% by weight of the detergent composition and wherein the hexahydrate coating comprises from about 6 to about 12% on a molar basis of each hexahydrate-encapsulated anhydrous sodium tripolyphosphate granule.

8. A process for preparing a detergent tablet of claim 1 which comprises the steps of 1) treating anhydrous granular sodium tripolyphosphate of a particle size such that substantially all will pass a standard 6 mesh screen (Tyler) and at least about will remain on a standard mesh screen (Tyler) with sutficient atomized spray water to hydrate to the hexahydrate state from about 2 mole percent to about 15 mole percent of said anhydrous granular sodium tripolyphosphate and to hydrate to the hexahydrate state substantially all of the anhydrous sodium tripolyphosphate which forms the surface of each granule to thereby form anhydrous sodium tripolyphosphate granules having a surface coating of sodium tripolyphosphate hexahydrate,

*(2) mixing together the hexahydrate surface-coated anhydrous sodium tripolyphosphate granules with the balance of the detergent composition comprising the synthetic detergent, water and sufiicient additional sodium tripolyphosphate detergency builder to bring the total amount of said builder in the tablet to from about 25 to about 85 by weight, thereby forming a uniform mixture in which the hexahydrate-encapsulated anhydrous sodium tripolyphosphate granules are substantially uniformly distributed throughout said mixture, and

(3) thereafter, compressing said detergent mixture into the desired shape.

9. The process of claim 8 wherein said hydration is effected by spraying atomized water onto a moving or agitated bed of anhydrous granular sodium tripolyphosphate.

10. The process of claim 8 wherein the synthetic detergent is added in the form of spray-dried detergent granules.

11. A process for preparing a detergent tablet of claim 1 which comprises the steps of 1) passing anhydrous granular sodium tripolyphosphate of a particle size such that substantially all will pass a standard 6 mesh screen (Tyler) and at least about 95% will remain on a standard 100 mesh screen (Tyler) through a humidifying zone to hydrate to the hexahydrate state from about 2 mole percent to about 15 mole percent of said anhydrous granular sodium tripolyphosphate and to hydrate to the hexahydrate state substantially all of the anhyrous sodium tripolyphosphate which forms the surface of each granule to thereby form anhydrous sodium tripolyphosphate granules having a surface coating of sodium tripolyphosphate hexahydrate,

(2") mixing together the hexahydrate surface-coated anhydrous sodium tripolyphosphate granules with the balance of the detergent composition comprising the synthetic detergent, water and sufficient additional sodium tripolyphosphate detergency builder to bring the total amount of said builder in the tablet to from about 25% to about 85% by weight, thereby form- 5 ing a uniform mixture in which the hexa'hydrateencapsulated anhydrous sodium tripolyphosphate granules are substantially uniformly distributed throughout said mixture, and

(3) thereafter, compressing said detergent mixture into 10 the desired shape.

14 References Cited UNITED STATES PATENTS 3/1963 Laskey 252-135 2/1968 Van Kampen 252-137 LEON D. ROSDOL, Primary Examiner P. E. WILLIS, Assistant Examiner US. Cl. X.R. 252-161 

